In photoelectric conversion devices such as solar cells that convert sunlight and the like into electricity, a positive electrode and a negative electrode are formed on the respective sides of a semiconductor layer having a junction, and positive and negative carriers generated in the semiconductor layer are collected to the respective electrodes to output them outside. When light absorption of the semiconductor layer is low, light that is not converted into electricity passes through the semiconductor layer, resulting reduction in efficiency. Hence, the photoelectric conversion efficiency is improved by reflecting back to the semiconductor layer the light having been passed through. To reflect the light, the back electrode on the opposite side to incident sunlight with respect to the semiconductor layer is generally formed of a high reflective metal electrode. Furthermore, a transparent conductive layer is sometimes sandwiched between the semiconductor layer and the back electrode.
Patent Document 1 discloses a structure for enhancing efficiency of a thin-film silicon solar cell, in which a refractive-index adjusting layer, which is formed of a material having a refractive index smaller than the transparent conductive layer formed on the front side of the back electrode, is sandwiched between the back electrode and the transparent conductive layer. For example, when the transparent conductive layer is formed of a gallium-doped zinc oxide (GZO), a silicon dioxide (SiO2) layer is sandwiched between the back electrode formed of silver (Ag) and the transparent conductive layer, thus reducing light that penetrates into and is absorbed by the back electrode and improving the light reflectance of the back electrode.
Patent Document 2 discloses a solar cell that includes a front electrode layer, a back electrode layer, and deposited layers that are sandwiched between the front electrode layer and the back electrode layer, wherein the deposited layers include a first photoelectric conversion layer and a reflection layer that reflects toward the first photoelectric conversion layer a part of light having passed though the first photoelectric conversion layer. The reflection layer is formed of a low refractive-index layer containing a refractive-index adjusting material and a contact layer sandwiched between the low refractive-index layer and the first photoelectric conversion layer. The refractive-index adjusting material is formed of a material having a refractive index lower than the material that the contact layer is formed of, so that the refractive index of the low refractive-index layer is smaller than that of the contact layer. This enhances the reflectance to a level higher than that of a conventional reflection layer consisting primarily of ZnO.